High molecular weight linear polyesters and copolyesters of glycols and terephthalic or isophthalic acid have been available for a number of years. These are described inter alia in Whinfield et al., U.S. Pat. Nos. 2,465,319 and in Pengilly, 3,047,539. These patents disclose that the polyesters are particularly advantageous as film and fiber formers.
From U.S. Pat. Nos. 3,304,282; 3,396,142; 3,408,225; 3,437,632; 3,671,487 and 3,678,079, it is known to prepare glass fiber reinforced thermoplastics.
Also, it is known to add a foaming agent to thermoplastics as disclosed in U.S. Pat. Nos. 2,964,794; 3,268,636; 3,277,209; 3,290,261; 3,377,296; 3,436,446; 3,442,829 and British Pat. No. 838,824. However, none of these references discloses a composition comprising a polyester, a foaming agent and a filler selected from the group consisting of fibrous glass and a mineral or mixtures thereof, which can be foam molded.
It has been discovered that the instant injection moldable composition comprising in admixture: (a) a polyester resin, (b) a filler selected from the group consisting of fibrous glass or a mineral or mixtures thereof in an amount of from about 5 to about 50 weight percent; and (c) a minor amount of a foaming agent, provides polyester products which have uniform cell structure, smooth surfaces, hign impact, modulus and tensile strength.
When a foaming agent is added directly to a polyester, highly irregular foaming occurs which results in an inferior product in that the product contains voids, sink marks. The product is also warped. However, when the foaming agent is added to a polyester containing a filler such as fibrous glass or a mineral or mixtures thereof in an amount of at least 5 weight percent, a foamed product is produced having a rigid cellular core within a solid integral skin.
The composition of the instant invention is injection molded in a standard injection molding machine to produce a variety of foam molded products.